772 C. B. BROWN ON THE ANCIENT 
5 feet. When an ordinary thick layer is left on the river’s edge— 
as is often the case, from the resistance it offers to the wearing action 
of the water and the protection it affords the clay on which it rests, 
—a dome-like pile of broken rock is left, having a formidable appear- 
_ ance, but which in reality is a very friable heap. One very curious 
form of this ironstone is seen in a clay-bed at Hytanahan, where 
it is in small, detached, smooth, hemispherical nodules, greatly 
resembling in form the iron slag from the bottom of a crucible. 
At Berury cliff, when the river stood at a level of 41 feet below 
the highest point it reaches in the rainy season, the following section 
(fig. 6) was observed :— 
Fig. 6.—-Section in the Berury Cliff, Purus River. 
t. Mottled clay. 2. Banded red and grey clay. 
3. Bluish clay, with layers of leaves. 
4, Bluish arenaceous laminated clay, probably of Tertiary age. 
The sections on the Jurua river are very similar to those on 
the Purus; and I therefore give only one section (fig. 7), which was 
taken at Gaviao Barreiras. 
Fig. 7.—Section at Gavivo Barreiras, Jurua River. 
River-deposit : Older deposit, probably Tertiary : 
1. Red loam. 6. False-bedded blue clay, containing imbedded leaves. 
2. Grey clay. 7. Grey laminated clay. 
3. Reddish clay. 8. Clay conglomerate, of masses of yellow sand and pink clay, 
4. Yellow clay. coated with crust of iron oxide, imbedded in yellow sand. 
5. Grey clay. 9. Red sand. 
I will now conclude the description of the various sections of the 
old river-deposit by recording one which occurs on the Javary at 
Santa Rosa:—10 feet red loam; 30 feet white sand. 
